Copyright isn't level legal vs illegal, it's infringing vs non-infringing. Fan art very often could be argued to be infringing, but no company has any reason to pursue it in the vast majority of cases, so they just don't.
It's very confusing, especially when you have to consider trademark as related but separate.
>>jefftk+W6
Infringement carries both civil (noncriminal) and criminal proscriptions and liabilities under much law, e.g., under US law, 17 USC Chapter 5:
>>jefftk+W6
It's civil vs criminal law. Illegal usually implies breaking a law and committing a crime. Copyright infringement is a civil matter, not criminal.
>>Taywee+Mf
It's unclear whether "here" refers to the artists spoofing Disney, or other actors pirating / duplicating artists' work for commercial use.
In the former case, I'd agree.
In the second, there's a clear violation of 17 USC 506(a)(1)(A).